This invention relates generally to modular flat panel display devices and particularly to a system for periodically reversing the order of video data in such systems.
A modular flat panel display device in which the instant invention can be utilized is described in U.S. Pat. No. 4,117,368 issued to F. J. Marlowe, et al. The Marlowe device consists of an evacuated envelope which is divided into channels by a plurality of insulating vanes. Each of the channels includes guide meshes for propagating electron beams along the lengths of the channels. When a particular line of the visual display is to be produced, the electron beams are ejected from the guide meshes and travel toward the display screen. The vanes support deflection electrodes which are biased with varying deflection potentials. These deflection potentials cause the electrons travelling from the guide meshes to the display screen to be scanned transversely across the channels. The electron beams of all the channels are simultaneously ejected from between the guide meshes so that a portion of the same horizontal line of the visual display is simultaneously generated across each of the channels. In order to avoid charging the capacitor formed by the deflection electrodes on opposite sides of a vane the same deflection voltage is applied to both deflection electrodes. Adjacent channels, therefore, are scanned in opposite directions. Video information, therefore, must also be supplied to adjacent channels in reverse order.
A system which reverses the order of data supplied to adjacent channels of a modular display device is described in U.S. Pat. No. 4,080,630 issued to F. J. Marlowe. In the Marlowe system, the incoming video data are in analog form and are digitized in an analog to digital converter. The digitized output of the A/D converter is supplied to a reversing shift register which is composed of two stages. The first stage includes a first shift register for each output bit of the digitized video signal. The second stage includes a second shift register for each output bit of the digitized video signal. The first and second shift registers are coupled through switching means to a primary shift register so that either the first or second shift register can load the primary shift register. When the switching means is coupled to the first register, the data are read out serially and directly provided to the primary register. When the switching means is coupled to the second shift register, the data are loaded from the first shift register to the second shift register in parallel form. The second shift register then provides the data to the primary register in an order reversed from the received order. Accordingly, a portion of the digitized data is loaded into the primary register in the same order as received and the other portion is loaded in the reverse order. The Marlowe system, therefore, is rather complex in that the data reversal required the utilization of two shift registers. Additionally, the use of the two shift registers requires precise clocking every 16 pulses in order to alternately load both registers.